(1) Field of the Invention
The invention relates to an electric motor having an ironless winding with externally or permanently excitable magnetic poles.
(2) Description of Related Art
Electric motors are used more and more frequently in many applications. The electro-mechanical energy in such motor is converted either with permanent excitation using permanent magnets or with external excitation using two separate coil arrangements in the rotor and stator, as disclosed for example in DE 69 735 825 T2. Losses occur during this energy conversion, which are essentially composed of ohmic losses, eddy current losses, hysteresis losses and friction losses.
The use of a high number of turns enables high power output, however at the expense of increased ohmic losses. The more winding material is used, the greater is the ratio of mechanical power output to consumed electric power the opposite occurs in generators operation).
The windings are typically constructed of a stator composed of motor iron with slots, in which the individual phase windings are laid or pole pieces, around which the phase windings are wound.
In addition, ironless winding arrangements, for example, embedded in hardened resin or having a self-supporting construction are known from DE 34 017 76 A1 and DE 27 44 145 C1.
Furthermore, slot-less stator designs are known, for example, from DE 69 407 908 12, DE 44 145 27 C1, and DE 69 735 825 T2 C1.
The arrangement of the winding in the air gap between rotor and stator is known, for example, from DE 41 300 16 A1, DE 120 606 7 B, DE 340 177 6 A1, DE 44 145 27 C1, and DE 69 735 825 T2.
Since the magnetic field in the windings of the electric motor varies over time, eddy current losses occur in the form of heat, which is dissipated in the iron parts of the motor. Contemporary electric motors use in part insulated stacks of sheet metal to reduce spreading of the eddy currents. The manufacture of these laminated stators is relatively expensive and these stators are not always offered by the various manufacturers. In addition, permanent-magnet electric motors are increasingly produced which, however, are unsuited for asynchronous motors. A winding can be replaced by employing permanent magnets, thereby reducing ohmic losses and increasing the energy efficiency.
Furthermore, the absolute motor weight and the motor dimensions, both of which are determined by the size and shape of the stator and the rotor as well as the windings, are of great importance for many applications, especially for mobile drive applications.